Conventionally, inkjet printers have been used to print an image onto printing paper by moving the printing paper relative to a head unit and ejecting fine droplets of ink from a plurality of outlets of the head unit toward the printing paper. An inkjet printer that carries out color printing is provided with a plurality of head assemblies that respectively correspond to inks of a plurality of colors. Each of the head assemblies has, for example, a plurality of heads arranged in a staggered configuration, each of the heads including a plurality of outlets.
Japanese Patent Application Laid-Open No. 2012-6267 (Document 1) discloses an inkjet recording apparatus that includes four connected heads for ejecting inks of black, cyan, magenta, and yellow, respectively. Each of the connected heads has a plurality of chips arranged in a direction (hereinafter, referred to as an “arrangement direction”) that intersects a direction of conveyance of a recording medium. Each of the chips has a plurality of nozzles for ejecting droplets of ink arranged at equal pitches in the arrangement direction. In the connected heads, the chips are arranged in a staggered configuration such that each two chips adjacent in the arrangement direction overlap partly with each other in the conveyance direction. In such an inkjet recording apparatus, a plurality of nozzles are aligned in the conveyance direction in areas where chips overlap with each other. Thus, a line that extends in the conveyance direction can be recorded by ejecting droplets of ink alternately from a plurality of nozzles.
Here, a configuration of the above head assemblies is conceivable in which heads each having outlets arranged such that the pitch of outlets in opposite longitudinal end portions is greater than that in a central portion are arranged in a staggered configuration in the arrangement direction as in Document 1. In this case, at the time of assembly of the head assemblies, a plurality of heads are positioned and fixed such that in end portions of each two heads that overlap with each other in the movement direction, the outlets of one head are each disposed between the outlets of the other head in the movement direction. In this way, in the range of overlap between the two heads, outlets are interpolated in positions where there are no outlets of these heads so as to make the pitch of outlets in the overlapping range equal to that in the central portion of the heads.
In the case of an inkjet printer where high resolution is required, however, the arrangement pitch of outlets is very small and thus there is a limit to the accuracy of alignment at the time of fixing the heads. If the mounting positions of two heads are displaced from design mounting positions, in the overlapping range between the heads, the outlets of one head that are interpolated between the outlets of the other head will be displaced, producing a plurality of ranges in which there are no outlets in the movement direction of printing paper. This consequently produces a plurality of voids extending in the movement direction on the printing paper and reduces print quality.